The Cornelia Pluton was previously found to have been faulted in two (Gilluly, 1946). The downthrown apex is host to a copper ore-body, and the upthrown block represents a vertical cross-section of the igneous system. Field work confirmed the character of the relationship between three texturally-distinct quartz monzonites described by Wadsworth (1968). Plagioclase crystals were chosen from all the phases, including previously undescribed hydrothermal rocks, and analyzed with a microprobe. Graphs of anorthite content versus radial distance revealed systematic patterns of compositional variation, analysis of which yielded a consistent, time-dependent model for the emplacement and crystallization of the system. The granodiorite resulted from an earlier intrusive event. The quartz monzonites crystallized initially downward from the system's roof, and, subsequently, upward from the floor. Saturation of the remaining pocket(s) of magma led to the development of an inner fine-grained phase, and possibly, the evolution of hydrothermal fluids. The genetic connection between these fluids and eventual mineralization of the cupola is suggested.

No description available.

No description available.

Ground magnetic data are consistent with the interpretation that Lower Jurassic volcanic rocks of the Twin Buttes mine area (Ox Frame Volcanics) are confined to a distinct block by the northwest trending Sawmill Canyon Fault Zone which was initially active during the Lower Jurassic. Possible reactivation of the Sawmill Canyon Fault zone in the Middle Jurassic as a left-lateral wrench fault is recorded by the deposition of syntectonic red-beds (Rodolfo Formation). Lower Cretaceous rocks (Whitcomb Quartzite, Glance Conglomerate, and Angelica Akrose) were deposited in alluvial environments resulting from additional reactivation of the Sawmill Canyon Fault Zone. Upper Cretaceous (Laramide) deformation involved the formation of northwest trending folds and northwest and northeast trending reverse, tear, and later block faults during the uplift of Precambrian basement. Ore deposits of the Pima mining district are localized along a northeast trending fault zone with evidence for initial activity in the Middle Jurassic and later reactivation during the Laramide.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.